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What is the purpose of three wires on a brushless motor??

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What is the purpose of three wires on a brushless motor??

Old 01-14-2009, 11:45 PM
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Default What is the purpose of three wires on a brushless motor??

Why is there three wires on a brushless motor instead of two??
Old 01-14-2009, 11:50 PM
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Default RE: What is the purpose of three wires on a brushless motor??

Positive, Negative, Sensor wire.
Old 01-14-2009, 11:56 PM
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Default RE: What is the purpose of three wires on a brushless motor??

Third wire is used for feedback is the simple answer...
Old 01-15-2009, 12:46 AM
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Default RE: What is the purpose of three wires on a brushless motor??

It uses the same concept as a 3 pole armature, except that in a brushless motor, the "armature" is sitting still. The ESC alternates current between the wires and that is what creates the push/pull that makes the magnet on the rotor spin.
Old 01-15-2009, 01:04 AM
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Default RE: What is the purpose of three wires on a brushless motor??

3 is better than 2, duh!
Old 01-15-2009, 04:14 AM
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Default RE: What is the purpose of three wires on a brushless motor??

With a Y(wye)-wound motor, three phases and three coils, each wire goes to one end of the three coils, the other end of the coils are joined to a common point. The switching is done as part of the ESC, so you need all three wires brought out.

http://en.wikipedia.org/wiki/File:Wye-delta.svg

With brushed, you have a mechanical switch inside the motor itself so you will only need two wires to apply power to the motor, like any other load (+V and GND).

When a brushless motor has only two wires (ie. a computer cooling fan) this is b'cos the ESC is integrated into the motor, and/or the motor may not be a three-phase motor.
Old 01-15-2009, 05:26 AM
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Default RE: What is the purpose of three wires on a brushless motor??

like access said...
no there isnt a sencor wire like chris was going on about...

there are 3 phases.
if you want to understand then read on...

the ESC's job is to compute all of the math to time the power pulses to each winding in the motor.
by giving it different combinations to each wire it can tell the motor which way to move...

if you were to apply power directly to wire A and B then the motor will jump to a posission and stay there, then change the combination and the motor will turn to the next posission in the line, switch combinations and the motor will change again.
there are 3 forward combinations i belive and 3 reverse combinations.
they are in a triangle configeration (basicly) and the rotor will be pushed around from each magnetic field as it turns on and then off again.

a brushed motor does the same...but it's combinations are controlled by the comutator which turn on a coil just ahead of where the rotor is at that point in time.

a brushless ESC is pretty cool really...
it has to GUESS what start up algorithim to use then turn on phase AB then AC then BC repeat, as you increase the throttle it needs to advance the timing and power accordingly.

make sence..this is only a basic explanation here and it gets a lot worse with the understanding on the Y and D winds then there's the rotor's "poles" and slotted stators etc etc[:@]

shaun
Old 01-15-2009, 10:15 AM
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Default RE: What is the purpose of three wires on a brushless motor??

Wow, typical internet forum answers here. Couple of grossly incorrect answers and finally someone steps in and gives good info.
Old 01-15-2009, 10:23 AM
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Default RE: What is the purpose of three wires on a brushless motor??

A brushless ESC is a very complicated thing, especially if sensorless.
This gives you the basic idea.

http://ww1.microchip.com/downloads/e...tes/00857a.pdf

And a good zero-rpm startup algorhythm doesn't involve guessing at all. It cycles through the phases at relatively high power in very quick succession, in order to get the rotor moving forward. This way the rotor starts smoothly and won't jump backwards or anything like that. It's not the most efficient way to start a motor, though. Once the rotor is moving, it can use the back-EMF sensing to know its position.

It's not 'typical internet' as much as 'heard it at the track' and 'heard it at the LHS'. There's a lot of misinformation out there, and when a racer who is doing well or the "always knowledgeable" staff at the LHS claim something, too many people will take it as a matter of faith. It might get perpetuated elsewhere on the internet, but something like that gets shot down pretty quickly on these boards.

Anyways if you read the appnote link I gave above, it does mention "Floating terminal BEMF".

"Figure 7 shows the equivelent circuit of the motor with coils B and C driven while coil A is undriven and available for BEMF measurement." etc. In other words, with Y-wound configuration, a common type of BEMF-sensing ESC, at any given phase, will be driving a coil with two wires and using the third to sense BEMF. Anyways the appnote describes it in much more detail than I can explain here.
Old 01-15-2009, 10:52 AM
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Default RE: What is the purpose of three wires on a brushless motor??

I was under the understanding that two of the wires power the motor and the third wire gets feedback in the form of voltage form the motor spinning.....this how the esc knows what the motor is doing.....is this close? and if it is then in away it is kinda right calling it a sensor wire.
Old 01-15-2009, 10:56 AM
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Default RE: What is the purpose of three wires on a brushless motor??

Even in that particular setup, it's not called the 'sensor wire' b'cos it's not used that way most of the time.

3 wires (A B C) and 3 phases (1 2 3).

1) A is powered, B is grounded, C is sensed.
2) B is powered, C is grounded, A is sensed.
3) C is powered, A is grounded, B is sensed.

There is no 'sensor wire' or even 'power wires' b'cos they change every phase. Wires only spend a third of their time being sensor wires, so it doesn't make sense to call a specific wire a 'sensor wire'.
Old 01-15-2009, 11:11 AM
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Default RE: What is the purpose of three wires on a brushless motor??

I think the problem may be that not everyone wants, needs or can understand the real explanation into everything. some people just want a simple answer. there are 3 wires because it's a 3 phase brushless system. at any given time two provide power and the other is a sensor. So even though they may split their time doing each, at a split second in time two provide power and the third is a sensor.

realistically, i don't think the OP wanted the electrical and mathematical explanation into WHY or HOW the motor or esc works. he asked a simple question, "why 3 wires" the simple and somewhat inaccurate answer is "sensor wire". I see NOTHING wrong with this.

If someone wanted a dissertation or PhD paper on the topic of brushless motors and escs they can frame their question that way.

ORIGINAL: GravityJunkie

Wow, typical internet forum answers here. Couple of grossly incorrect answers and finally someone steps in and gives good info.
The first answers were not "grossly inaccurate" they were simplified. I'm not just saying that because mine was one of them, I'd be saying this regardless of who wrote the first answers and the others.

If a kid asks the question, "why is the sky blue", do you get into a discussion of wavelengths, atmosphere.. etc?
Old 01-15-2009, 01:07 PM
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Default RE: What is the purpose of three wires on a brushless motor??


ORIGINAL: Druss
The first answers were not "grossly inaccurate" they were simplified. I'm not just saying that because mine was one of them, I'd be saying this regardless of who wrote the first answers and the others.

If a kid asks the question, "why is the sky blue", do you get into a discussion of wavelengths, atmosphere.. etc?
ChrisRC post was pretty off. The sensor wire is a separate wire, not included on all brushless systems.
Old 01-15-2009, 01:16 PM
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Default RE: What is the purpose of three wires on a brushless motor??


ORIGINAL: GravityJunkie

Wow, typical internet forum answers here. Couple of grossly incorrect answers and finally someone steps in and gives good info.
Looks like a high post counts represents low IQ.
Old 01-15-2009, 01:33 PM
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Default RE: What is the purpose of three wires on a brushless motor??


ORIGINAL: Access

Even in that particular setup, it's not called the 'sensor wire' b'cos it's not used that way most of the time.

3 wires (A B C) and 3 phases (1 2 3).

1) A is powered, B is grounded, C is sensed.
2) B is powered, C is grounded, A is sensed.
3) C is powered, A is grounded, B is sensed.

There is no 'sensor wire' or even 'power wires' b'cos they change every phase. Wires only spend a third of their time being sensor wires, so it doesn't make sense to call a specific wire a 'sensor wire'.
I said kinda like a sensor wire which is true for a split second....I didnt know that it changed form wire to wire..you learn something new everyday...great discussion.
Old 01-15-2009, 01:46 PM
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Default RE: What is the purpose of three wires on a brushless motor??

A typical person spends between a third and a fourth of their time sleeping, does that mean we should call people 'sleepers' or that a person is defined by sleeping? That the third wire is a 'sensor wire' is not a defining characteristic, for example:

sensored implementations, which use a hall-effect sensor on the rotor rather than back-EMF sensing, do not use third wire to sense at all. Instead they use a bunch of wires coming out of this hall-effect sensor.

'dumb' implementations that use no feedback at all, though rarely seen in the RC car market.
etc.

But honestly it becomes an exercise in futility, the most proper thing to do is to call the terminals "A, B, and C" b'cos their defining characteristic is that they are used to deliver power to the coils.

And no need to name names or indulge in ad-hominem attacks, seriously people.
Old 01-15-2009, 01:57 PM
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Default RE: What is the purpose of three wires on a brushless motor??

Good thread, actually. Basic how-does-it-work question. Exposed some of the misconceptions about how a lot of people perceive these motors work, and produced some good answered presented in an easy to understand way. Even a little theory on how the misconceptions come about!

Could also use a picture of the leads coming of the windings, people will see that it each lead just comes off different bundles of wires, and appear to be an extension of those wire strands.
Old 01-15-2009, 02:04 PM
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Default RE: What is the purpose of three wires on a brushless motor??

does that mean we should call people 'sleepers'

wasn't that a scary movie....
Old 01-15-2009, 02:19 PM
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Default RE: What is the purpose of three wires on a brushless motor??

I got it!!!! Because somebody put 3 wires on the speed control? Ha! I heard the third wires senses the voltage and amp draw to let the esc know when to shut off. Is this partially true?
Old 01-15-2009, 04:02 PM
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Default RE: What is the purpose of three wires on a brushless motor??


ORIGINAL: Access
Once the rotor is moving, it can use the back-EMF sensing to know its position.
yep that's right access

no jet that's not right[&:]
any of the wires provide a little infomation back to the ESC (almost like it's generating power) when that wire ISNT being used as a power wire during the cycle.
the ESC itself has a brain board that usually operates on 6v and that tells the power board what to do, when to do it and when it's too hot and shut down. basicly.

shaun
Old 01-15-2009, 08:25 PM
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Default RE: What is the purpose of three wires on a brushless motor??

I'm going to wander slightly on a tangent and ask if some type of 'converter / adapter' exists to allow a brushless motor to run on a brushed ESC?

I believe I have seen a small circuit board that is wired between the ESC and the motor in airplane applications.

Correct me if I'm wrong but isn't that how the Losi micro BL motors work? The factory brushed ESC is used in conjunction with a secondary module that takes the power of the two ESC motor wires, utilizes some electronic wizardry and sends out phased electric pulses to power a brushless motor.

I was curious if this type of technology exists for 1/10 applications. Any thoughts?
Old 01-15-2009, 11:52 PM
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Default RE: What is the purpose of three wires on a brushless motor??

ORIGINAL: Druss
The first answers were not "grossly inaccurate" they were simplified. I'm not just saying that because mine was one of them, I'd be saying this regardless of who wrote the first answers and the others.

If a kid asks the question, "why is the sky blue", do you get into a discussion of wavelengths, atmosphere.. etc?
Massively simple explainations do nothing to answer a question. And in fact, actually hinder better understanding.

If the post would have stated that each wire takes a turn being positive, negative and sensor, it would have been good. Heck, if I were new to RC and saw that post, I'd think there was only one way to hook up a brushless motor. Because of a lack of details, that post is grossly inaccurate.

If a kid asks that question, yes I would tell him it is because of the way light that reaches your eyes. Give'em enough details. A person without the details is just a fool...
Old 01-16-2009, 02:34 AM
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Default RE: What is the purpose of three wires on a brushless motor??


ORIGINAL: drumin_nut

I'm going to wander slightly on a tangent and ask if some type of 'converter / adapter' exists to allow a brushless motor to run on a brushed ESC?

I believe I have seen a small circuit board that is wired between the ESC and the motor in airplane applications.

Correct me if I'm wrong but isn't that how the Losi micro BL motors work? The factory brushed ESC is used in conjunction with a secondary module that takes the power of the two ESC motor wires, utilizes some electronic wizardry and sends out phased electric pulses to power a brushless motor.

I was curious if this type of technology exists for 1/10 applications. Any thoughts?
no there isnt a module...in hte losi micro's u have to replace the reciver/ESC combo thing with a normal micro reciver and a very small brushless ESC.

there is no converter avalible that i know of and it's pretty pointless if there was.
as you need a brain board and a power board to supply the power to each phase at the right time.
shaun
Old 01-16-2009, 12:42 PM
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Default RE: What is the purpose of three wires on a brushless motor??

I believe I have seen a small circuit board that is wired between the ESC and the motor in airplane applications.

That IS the ESC.

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